title: Diastereodifferentiating photocyclodimerization of 2-anthracenecarboxylates tethered to a cyclic tetrasaccharide scaffold: critical control of photoreactivity and stereoselectivity.
abstract: From a complex mixture of mono- and di-2-anthracenecarboxylic acid (AC) esters of cyclic nigerosylnigerose (CNN), two monoesters (2(B) and 6(A)) and four diesters in which AC was introduced on the transannular B/D (2(B)2(D)), adjacent A/B and A/D (6(A)2(B) and 6(A)2(D)), and same B/B (2(B)3(B)) nigerose rings were isolated. Possessing two ACs at distant positions, 2(B)2(D) and 6(A)2(D) showed negative Cotton effects for the (1)Bb band, the intensities of which were stronger than that of 6(A). 2(B)2(D) and 6(A)2(D) slowly photocyclodimerized to give HH dimers 3* and 4 with 57% and 81% HH selectivity, respectively, which were appreciably higher than that for 6(A) (34%), while the enantiomeric excesses (ee's) of anti-HH dimer 3* were 2% and -18%, respectively. In contrast, 6(A)2(B) and 2(B)3(B) carrying two ACs on adjacent A and B rings or at vicinal positions on the B ring, respectively, exhibited strong positive CD couplets, the amplitudes of which amounted to 97 and 409 M(-1) cm(-1), respectively. Upon irradiation, 6(A)2(B) afforded 3* with -62% ee and 4 in 96% combined yield, whereas 2(B)3(B) gave almost exclusively 3* with -99% ee in 96% yield, likely as a result of the introduction of two ACs at the vicinal positions of the rigid CNN scaffold.
authors.affiliation: Department of Applied Chemistry, Osaka University , 2-1 Yamada-oka, Suita 565-0871, Japan.
authors.forename: Gaku
authors.initials: G
authors.lastname: Fukuhara
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Nakamura
authors.forename: Yuko
authors.initials: Y
authors.lastname: Kawanami
authors.forename: Cheng
authors.initials: C
authors.lastname: Yang
authors.forename: Tadashi
authors.initials: T
authors.lastname: Mori
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Hiramatsu
authors.forename: Yasufumi
authors.initials: Y
authors.lastname: Dan-oh
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Nishimoto
authors.forename: Kazuo
authors.initials: K
authors.lastname: Tsujimoto
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Inoue